Why would you perform a rolling NPV calculation?

Much earlier this semester, I said the three things listed below, explain, in detail, why each one of these is correct and$/$or true.

Cash Flow is king

Keep your tax base low

Depreciation is your friend

Why does a loan pay off faster if you make extra payments? Show this with an example calculation.

What is the weighted average cost of capital for a firm which has a debt$-$to$-$equity ratio of $2$:$3$ and a beta of $2\mathrm{.}3.$ The risk free rate is $4\mathrm{.}5\%$ and the market risk premium is $8\mathrm{.}5\%$; the corporate tax rate is your age in years $($i$.$e$.$ my tax rate is $61\%).$